Bayer's prescription drug sales grew by more than 8% last year, and analysts worry that growth isn't sustainable as the company socks billions into buying ag giant Monsanto.

Bayer’s pharma products have been growing lickety-split, and its 2016 numbers show just how—and how much. Prescription drug sales expanded by 8.7% last year, to €16.4 billion, the company said in its annual earnings release, and once again, its usual suspects are behind the surge.

What’s ahead for the burgeoning healthcare business—that’s the question. Though Bayer has put up a solid growth forecast for those units in 2017, sales-wise, and pledges to boost margins in all three, analysts worry that the company’s focus on its Monsanto buyout will drain away resources. The company might not have the capital to put into R&D programs like those that produced the blockbuster anticoagulant Xarelto and vision treatment Eylea, they worry.

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The Monsanto deal marks a “lost opportunity to develop the pharma pipeline,” Bernstein analyst Ronny Gal wrote last year, noting that “Bayer does not have the funds to invest in both Ag and Pharma at the same time.”

That’s ironic, considering the billions that those drugs have been ginning up for the company over the past few years. Take Xarelto, for one, which Bayer sells outside the U.S. It grew by 30% last year, in currency-adjusted terms, thanks to higher script numbers in Europe and Japan. The German company also collected bigger licensing revenues on the drug from U.S. partner Johnson & Johnson. Total? Almost €3 billion. Eylea, for its part, delivered €1.62 billion, up 32%.

Together, those two drugs and three other newer Bayer meds—colon cancer med Stivarga, prostate cancer radiotherapy Xofigo and pulmonary arterial hypertension remedy Adempas—are expected to add up to €6 billion this year.

But beyond that, Bayer faces pressure on its hemophilia franchise as other drugmakers roll out competing products, and it’s been a reliable revenue-generator. Kogenate/Kovaltry, for instance, brought in blockbuster-plus sales for 2016—flat year-over-year. Its older multiple sclerosis drug is also on the decline as it loses exclusivity in various markets and faces new competition, with sales down more than 10% to €734 million. Nexavar, which still brings in hefty sales—€830 million for the year—faces a patent loss in 2020 and might have to deal with generics sooner if challenger Mylan has its way.

And Stivarga itself is seeing declines. A new rival, Lonsurf from Japanese drugmaker Otsuka, was approved in October 2015, and it has since played a part in eroding Stivarga sales. Last year, the Bayer med took a 12% drop, to €275 million.

Right now, Bayer doesn’t have much in the way of new candidates to come in and back up Xarelto when that drug goes off patent in 2024, much less Nexavar.

In short, Bayer will need R&D investment on the pharma side to beef up healthcare sales in the long term. Consumer health, which Bayer had hoped to push after buying Merck & Co.’s unit in 2014, and animal health may be growing, but much more slowly than pharma.

BMI Research’s Craig Smith is another analyst worried that Bayer won’t be able to deliver enough new drugs in the coming years. Smith has pointed out that the company already spends less than its Big Pharma peers do on R&D. With that in mind, the Monsanto “deal could significantly weaken” Bayer’s “capacity to grow within the pharmaceuticals space.”

Bayer’s top-selling drugs have kept the company on a positive trajectory in recent years. Letting its pipeline falter because it’s spending money and time on a Crop Science merger would be a long-term mistake.